Composite flame barrier laminate for a thermal and acoustic insulation blanket

ABSTRACT

A multilayer laminate comprising a first polymeric film layer capable of withstanding a temperature of at least 200 C for at least 10 min, a first adhesive layer having an areal weight of from 2 to 40 gsm capable of activation at a temperature of from 75 to 200 degrees C., an inorganic refractory layer, a second adhesive layer having an areal weight of from 4 to 40 gsm capable of activation at a temperature of from 75 to 200 degrees C. and a second polymeric film layer capable of withstanding a temperature of at least 200 C for at least 10 min, wherein at least one of the first or second polymeric film layers is thermoplastic.

This application is a continuation in part of application Ser. No.12/759,741 filed on Mar. 14, 2010 which claims priority from provisionalfiling application No. 61/171,163 filed on Apr. 21, 2009.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention pertains to a composite laminate having flame resistantproperties. The invention also covers use of the composite laminate in athermal and acoustic blanket as may be found in an aircraft fuselage ora turbine engine compartment.

2. Background of the Invention

U.S. Pat. No. 6,322,022 to Fay et al. discloses burnthrough resistantsystems for transportation especially aircraft.

U.S. Pat. No. 6,670,291 to Tomkins and Vogel-Martin describes a laminatesheet material for flame barrier layer applications.

There remains an ongoing need for thermal and acoustic blankets foraircraft structures having reduced weight and improved resistance toflame spread.

SUMMARY OF INVENTION

This invention is directed to a multilayer laminate for use as a flamebarrier comprising:

-   (i) a first polymeric film layer capable of withstanding a    temperature of at least 200 C for at least 10 min,-   (ii) a first adhesive layer having an areal weight of from 2 to 40    gsm capable of activation at a temperature of from 75 to 200 degrees    C.,-   (iii) an inorganic refractory layer,-   (iv) a second adhesive layer having an areal weight of from 2 to 40    gsm capable of activation at a temperature of from 75 to 200 degrees    C., and-   (v) a second polymeric film layer capable of withstanding a    temperature of at least 200 C for at least 10 min, wherein at least    one of the first or second polymeric film layers is thermoplastic.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross section through a burnthrough resistantcomposite laminate of this invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a section through a burnthrough resistant compositelaminate 10 comprising a first polymeric film layer 11, a first adhesivelayer 12, an inorganic refractory layer 13, a second adhesive layer 14and a second polymeric film layer 15.

Polymeric Film Layer

At least one of the first or second polymeric film layers isthermoplastic. The other polymeric layer may be thermoset. Preferablyboth polymeric layers are thermoplastic. The polymeric film layers mustbe capable of withstanding a temperature of at least 200 C for at least10 min.

Preferably the film layer has a UL 94 flame classification of V-0. UL 94flame classification is an Underwriters Laboratory test, The Standardfor Flammability of Plastic Materials for Parts in Devices andAppliances, which measures a material's tendency either to extinguish orto spread the flame once the specimen has been ignited. V-0 indicatesthat the material is tested in a vertical position and self-extinguishedwithin ten seconds after the ignition source is removed.

A further requirement of the film layer is that it should have athickness in the range of from 4 to 30 micrometers. More preferably thethickness range should be from 5 to 15 micrometers and most preferablyin the range from 5 to 7 micrometers. The film layer provides mechanicalstrength and stiffness to the laminate.

Suitable film layer materials are polyketone, polyimide, polysulfone,polyarylene sulfide, fluoropolymers, liquid crystal polymers andpolycarbonate. Examples of polyketone are polyetheretherketone (PEEK)and polyetherketoneketone (PEKK). Polyethersulfone and polyphenylsulfoneare examples of polysulfone. Poly(p-phenylene sulfide is a suitablepolyarylene sulfide for use in this invention. Polyvinylfluoride (PVF)and polyvinylidinefluoride (PVDF) are examples of fluoropolymers. Asuitable fluoropolymer is available from E.I. du Pont de Nemours,Wilmington, Del. under the tradename Tedlar. Polyarylate is an exampleof a suitable liquid crystal polymer. Some of these films may also becoated with a second polymeric material. For example, a polyimide film,Kapton®, may be coated with fluorinated ethylene propylene, FEP and usedin this invention.

In a preferred embodiment, the film layers are PEEK or PEKK.

The surface of the film layer may optionally be treated to improveadhesion with another substrate such as an adhesive. Suitable surfacetreatment methods include, but are not limited to, corona etching andwashing with coupling agents such as ammonium, phosphonium or sulfoniumsalts.

In some embodiments, the film layer is metalized on at least onesurface. In some embodiments, the metalized surface is in contact withthe adhesive layer.

Adhesive Layer

The first and second adhesive layers are shown in FIG. 1 at 12 and 14respectively. The layers separate the first and second polymeric filmlayers from the refractory layer.

The adhesive layer may be a thermoplastic or thermoset resin. Thermosetresins include epoxy, epoxy novolac, phenolic, polyurethane, andpolyimide. Thermoplastic resins include polyester, polyetherketone,polyetheretherketone, polyetherketoneketone, polyethersulfone, andpolyolefin. Thermoplastic resins are preferred.

One of the objectives for having a high temperature polymeric filmadhesively bonded to a refractory layer is to provide mechanicalreinforcement and protection to the overall composite laminate duringmanufacturing, installation and service.

To prevent possible damage from mechanical stressing exerted by ashrinking/melting/disintegrating polymeric film on an inorganicrefractory film-like layer it is preferred that inter-ply bond of thecomposite laminate would fail (i.e. release/melt/soften) in the earlystage of the flame exposure thus causing internal de-bonding of thecomposite laminate (i.e. delamination of the refractory layer from thepolymeric film) before the polymeric film starts disintegrating. Due totheir relatively low activation temperatures, thermoplastic adhesivesare a preferred choice over thermoset adhesives for this application.

The adhesive layer may optionally contain up to 40 weight percent of aflame retardant ingredient. Suitable flame retardant ingredients includeantimony trioxide, halogenated flame retardants includingtetrabromobisphenol A, polybrominated biphenyls, Penta-, Octa-,Deca-brominated diphenyl ether (oxide) and hexabromocyclododecane.Phosphorus containing flame retardants are also widely used.

The adhesive must be capable of activation at a temperature in the rangeof 75 to 200 degrees C. In some embodiments, the activation range isfrom 120 to 140 degrees C. By activation we mean that for a thermosetresin, the resin must bond to the polymeric film layer and therefractory layer within the specified temperature range. For athermoplastic resin, activation means that the resin softens and flowssufficiently to bond to the polymeric film layer and the refractorylayer. The adhesive bond between the inorganic refractory layer and thefirst polymeric film is at least 0.5 lb/in. In some embodiments, theadhesive bond between the inorganic refractory layer and the firstpolymeric film is at least 0.8 lb/in. The adhesive bond between theinorganic refractory layer and the second polymeric film is at least0.25 lb/in. In some embodiments, the adhesive bond between the inorganicrefractory layer and the second polymeric film is at least 0.8 lb/in.

The adhesive layer weighs from 2 to 40 gsm. In some embodiments theadhesive layer weighs from 3 to 15 gsm or even from 5 to 10 gsm. If theadhesive weight is below 2 gsm, the bond strength will be too weak. Ifthe adhesive weight is greater than 40 gsm, unnecessary weight will beadded.

Refractory Layer

The inorganic refractory layer is on the opposite side of the adhesivelayer from the polymeric film layer as is shown at 13 in FIG. 1.

The refractory layer has a dry areal weight of from 15 to 50 gsm and aresidual moisture content of no greater than 10 percent by weight, Insome embodiments, the refractory layer has a dry areal weight of from 20to 35 gsm and a residual moisture content of no greater than 3 percentby weight. The layer

The refractory layer comprises platelets. Preferably at least 85% of thelayer comprises platelets, more preferably at least 90% and mostpreferably at least 95%. In some embodiments, platelets comprise 100% ofthe layer. The refractory layer may comprise some residual dispersantarising from incomplete drying of the platelet dispersion duringmanufacture.

In some embodiments, the refractory layer has a thickness of from 7.0 to76 micrometers and more preferably from 7.0 to 50 micrometers. In someembodiments, the refractory layer has a UL 94 flame classification ofV-0. The function of the refractory layer, in which adjacent plateletsoverlap, is to provide a flame and hot gas impermeable barrier. Theinorganic platelets may be clay, such as montmorillonite, vermiculite,mica, talc and combinations thereof. Preferably, the inorganic oxideplatelets are stable (i.e., do not burn, melt or decompose) at about 600degrees C., more preferably at about 800 degrees C. and most preferablyat about 1000 degrees C. Vermiculite is a preferred platelet material.Vermiculite is a hydrated magnesium aluminosilicate micaceous mineralfound in nature as a multilayer crystal. Vermiculite typically comprisesby (dry) weight, on a theoretical oxide basis, about 38-46% SiO₂, about16-24% MgO, about 11-16% Al₂O₃, about 8-13% Fe₂O₃ and the remaindergenerally oxides of K, Ca, Ti, Mn, Cr, Na, and Ba. “Exfoliated”vermiculite refers to vermiculite that has been treated, chemically orwith heat, to expand and separate the layers of the crystal, yieldinghigh aspect ratio vermiculite platelets. Suitable vermiculite materialsare available from W. R. Grace of Cambridge, Mass., under the tradedesignations MicroLite 963 and MicroLite HTS-XE.

The thickness of an individual platelet typically ranges from about 5Angstroms to about 5,000 Angstroms more preferably from about 10Angstroms to about 4,200 Angstroms. The mean value of the maximum widthof a platelet typically ranges from about 10,000 Angstroms to about30,000 Angstroms. The aspect ratio of an individual platelet typicallyranges from 100 to 20,000.

In some embodiments of this invention, the inorganic platelet layer isreinforced by a lightweight open weave fabric scrim either laid onto asingle platelet layer or placed between two layers of platelets so as toprovide additional mechanical strength to the layer. The scrim can bemade from natural, organic or inorganic fibers with glass, cotton, nylonor polyester being typical examples. A glass fiber scrim is particularlypreferred. The scrim may be a woven or knit structure and has a typicalareal weight not exceeding 40 grams per square meter.

In some embodiments, the refractory layer is perforated to enhancebonding to the adhesive layer. With a perforated refractory layer, theadhesive bond between the refractory layer and the polymeric film is atleast 1.0 lb/in. The extent of perforation is determined byexperimentation for each laminate assembly. In order to preventcompromising flame barrier properties, an individual perforation shouldnot exceed 2 millimeters in maximum dimension. In a preferableembodiment, individual perforations should be spaced at least 10millimeters apart. The shape of the perforations is not critical,Suitable perforations include circles, squares, rectangles, ovals andchevrons.

A refractory layer comprising platelets as herein described provides anonporous, flexible, film-like sheet or coating. The platelet layer isalso thin, dense and has a very smooth and tough surface, attributesthat assist in the heat sealing process when the laminate comprising therefractory layer is used in a thermal blanket. A refractory layercomprising ceramic fibers is much more porous, brittle, and friable.

In a preferred embodiment, the refractory layer further comprisescations arising from contact, at a temperature of from 10 to 50 degreesC., with an aqueous cationic rich solution at a cation concentration offrom 0.25 to 2N. The contact with the cationic solution occurs prior toassembling the refractory layer into the composite laminate. Thiscationic treatment provides enhanced stability to the refractory layeron exposure to fluids.

Flame Barrier

The composite laminate as described above may be used as a flame barrierlayer. In a preferred embodiment, the first polymeric film is facingoutwards, that is, away from the object being protected. Flame barrierlayers find use in applications in vehicles or building structures suchas aircraft, trains, boats and offshore rigs where the flame barrierlayers may be found in ceiling, sidewall and floor panels. For aircraft,other uses are in cargo liners and thermal acoustic blankets.

Thermal Acoustic Blanket

The flame barrier as described above may be used as a component in athermal insulation and acoustic blanket. An example of such a blanket isdescribed in United States Patent Application publication number2007/0155265 to Anderson. FIGS. 2 and 3 of this publication show at 16 afire-retardant barrier layer. The flame barrier layer of this inventioncould replace the flame barrier layers described in the Andersonpublication.

TEST METHODS

The 5-layer composite laminates were subjected to a flame test thatreplicated the temperature and air mass flux test conditions of testmethod FAA FAR 25.856(b), App. F, Part VII. Somewhat lower heat flux wascompensated with a higher air mass flux to replicate a requiredthermo-mechanical stress level to be exerted on the composite flamebarrier laminates during the burn-through test.

EXAMPLES

All parts and percentages are by weight unless otherwise indicated. Alltemperatures are in degrees C. unless otherwise indicated.

Inorganic Refractory Material

The inorganic refractory material used in all the Examples wasvermiculite. The vermiculite grade was a high solids version of anaqueous dispersion of Microlite® 963 having an “as supplied” solidscontent of 7.5 percent. The dispersion was obtained from W.R. Grace andCo, Cambridge, Mass. The vermiculite dispersion used in all the Exampleswas concentrated to a solids content of 10.7+/−0.1 weight percent.

Release Paper

The release paper used in all Examples was 11 mil thick hydrophilic grayRagKraft paper comprising a blend of 50 weight percent of cellulosefibers and 50 weight percent of cotton fibers. The paper was obtainedfrom Crocker Technical Papers, Fitchburg, Mass. The paper had a basisweight of 8.1 oz/sq. yd., an average thickness of 11.0 mil, a density of1.0 g/cu·cm., a Gurley Air Resistance of 714 sec/100 cc, 20 oz. cyl., asmoothness of 103 Sheffield units, a dry tensile strength of 122.0lb/in. in the machine direction and 40.0 lb./in. in the cross direction.The wet tensile strength was 6.4 lb./in. in the machine direction and2.5 lb./in. in the cross direction.

Preparation of an Inorganic Refractory Layer on a Film

Vermiculite dispersion concentrated to a solids content of 10.6 weightpercent was coated on 2 mil thick metalized polyester film using a slotdie coating system to form a refractory layer on the film. The film wasmetalized on one side. The coating was applied to the metalized side ofthe film. The film was obtained under the tradename Mylar from E.I.DuPont de Nemours and Co., Wilmington, Del. The coated film was dried inan oven at a temperature cycle of 15 minutes at 60 degrees, 15 minutesat 71 degrees, 15 minutes at 82 degrees, 15 minutes at 93 degrees, andover 15 minutes at 99 degrees. The refractory layer had a dry coatweight of 35 gsm and a moisture content of below 5%. After drying, thefilm layer was separated from the refractory layer and both layers werewound up on separate rolls.

Preparation of an Inorganic Refractory Layer on a Release Paper

Vermiculite dispersion concentrated to a solids content of 10.8% weightpercent was coated on RagKraft release paper using a slot die coatingsystem to form a refractory layer on the paper. The coated paper wasdried for 15 minutes in an air flotation oven at a temperature notexceeding 110 degrees C. until the inorganic refractory layer hadmoisture content below 5%. Differential drying temperatures were appliedto the top (vermiculite side) and the bottom (release paper side). Thedrying profile on the top side was 5 minutes at 49 degrees, 5 minutes at60 degrees and 5 minutes at 71 degrees. The drying on the bottom sidewas maintained for 15 minutes at 99 degrees. The refractory layer had adry coat weight of 33 gsm.

Polymeric Films

The polymeric film used as the first and second polymeric films in allexamples was a 6 micron thick polyetheretherketone (PEKK) film gradeDS-E obtained from Cytec Industries, Woodland Park, N.J.

Adhesives

The following adhesives were used to make the three layer laminate.Bostik brand products were obtained from Bostik Inc., Wauwatosa, Wis.

Ref (a)—Bostik 10-669-3, a 3 mil Phenoxy Urethane thermosetting 132 gsmfilm adhesive.

Ref (b)—Bostik LADH 402, a solvent-based polyamide flameretardantthermoplastic liquid adhesive.

Ref (c)—Bostik L7132R-75/Boscodur 24T, a two-component solvent basedthermosetting liquid adhesive system This is a linear saturatedpolyester based adhesive (L7132R), with polyisocyanate (Boscodur 24T) asa curing agent.

Lamination Equipment

For all Examples, a flat-bed double-belt laminator with a Teflon coatedfiberglass belt was used to form the composite laminates. The laminationtemperatures in the 9 foot long pre-nip heating section were 70 to 90degrees in zone 1, 90 to 110 degrees in zone 2 and 130 to 150 degrees inzone 3.

The lamination temp in the 3 foot long post-nip cooling section was 50to 70 degrees in zone 4.

The force applied by the belt on a sample size of 400 square centimeterswas 5 kN. The machine line speed was 2 m/min.

Example 1

The same adhesive was used as the first and second adhesives. Theadhesive used, LADH 402 (Ref. (b)), was deposited on the surface of thePEKK film, the first polymeric film, using a Gardco AdjustableMicrometer “Microm II” Film Applicator. After deposition, samples of thecoated film were dried in a conventional oven at 80 degrees for 10minutes to allow the solvent in the adhesive to evaporate. The weight ofadhesive deposited on the surface of the polymeric film was 8 gsm.

The adhesive coated film was bonded to the refractory layer on a releasepaper in the double-belt laminator with the adhesive contacting theexposed refractory surface to form 3-layer composite laminate. Therelease paper was removed from the laminate and, in the double-beltlaminator, the 3-layer laminate was bonded to the second polymeric filmby the second adhesive such that the second adhesive contacted theexposed refractory surface to form final 5-layer composite laminate. Thelaminate comprised in order a first polymeric film, a first adhesivelayer, an inorganic refractory layer, a second adhesive layer and asecond polymeric film. The laminate weight was 65 gsm.

When exposed to a flame, sample showed a good resistance to flamepropagation, with inorganic refractory layer acting as an effectiveflame barrier.

Example 2

This example was similar to Example 1 except that the thermosettingadhesive (Ref. (c)) was used as the first and second adhesives.

Curative 24T was mixed with 7132R resin with mixing ratio of 20-24volumes of 7132R to 1 volume of 24T. After blending into a homogenoussolution it was immediately deposited on the polymeric film and dried inan oven to allow solvent to evaporate. The weight of the adhesivedeposited on the surface of the polymeric film was 8 gsm.

The bonding process was as in Example 1. The laminate comprised in ordera first polymeric film, a first adhesive layer, an inorganic refractorylayer, a second adhesive layer and a second polymeric film. The laminateweight was 65 gsm.

On completion of bonding, the 5-layer laminate was exposed to a flame.The test sample showed a good resistance to flame propagation withinorganic refractory layer acting as an effective flame barrier.

Example 3

This was similar to Example 1 except that, prior to lamination, the 35gsm refractory layer had been coated onto polyester film andsubsequently separated from the film to give an unsupported refractorylayer.

The bonding process was as in Example 1. The laminate comprised in ordera first polymeric film, a first adhesive layer, an inorganic refractorylayer, a second adhesive layer and a second polymeric film.

On completion of bonding, the 5-layer laminate was exposed to a flame.The test sample showed a good resistance to flame propagation withinorganic refractory layer acting as an effective flame barrier. Thelaminate weight was 65 gsm.

A general observation was that during the bonding step in the doublebelt laminator, it was more difficult to handle an unsupportedrefractory layer than one supported by a release paper.

Example 4

Prior to lamination, the 35 gsm refractory layer had been coated ontopolyester film and subsequently separated from the film to give anunsupported refractory layer.

The first and second adhesive was Bostik 10-669-3 (Ref. (a)).

In this Example a single step bonding process in the double-beltlaminator was used to a 5-layer laminate. Materials were laid up into anassembly in the sequence of a first polymeric film, a first adhesivelayer, an inorganic refractory layer, a second adhesive layer and asecond polymeric film. This assembly was then run through the laminatorthus bonding the 5-layers into a unitary structure. The laminate weightwas 315 gsm.

On completion of bonding, the 5-layer laminate was exposed to a flame.The test sample showed a good resistance to flame propagation withinorganic refractory layer acting as an effective flame barrier. Withthe exception of a significantly higher weight of the final 5-layerlaminate of Example 4, the findings were very similar to those forExample 3. For some applications, the relatively high weight of Example4 at 315 gsm when compared to Example 3 at 65 gsm is a significantdisadvantage.

Example 5

This was similar to Example 1 except that, after coating and drying, the33 gsm refractory layer on a release paper was treated, at ambientconditions, with an aqueous cationic rich solution.

The coated release paper was immersed for one minute in a cation richsolution of sodium chloride dispersed in water at 0.5N concentrationthen air dried at 24 degrees C. for 2 minutes followed by additionaldrying for 30 minutes inside a conventional oven heated to 80 degrees C.

Once dried to about 3% moisture content, the cation treated material wasremoved from the oven. Excess dry sodium chloride that had accumulatedon the outer surfaces of the refractory layer and the release paper wascarefully wiped off with a dry soft cloth.

The cation treated refractory layer on release paper was then adhesivelybonded to PEKK film (Ref. 1) to form a 5-layer laminate in the samemanner as Example 1.

When compared to a non-cation treated refractory layer, the cationtreated layer showed a significantly improved stability when exposed toeither high humidity conditions for a prolonged time such as 120 hoursinside an aging chamber at 80 degrees C. and 90% RH or after immersionin water for at least 10 minutes. Other findings were similar to thoseof Example 1.

What is claimed is:
 1. A multilayer laminate for use as a flame barriercomprising (i) a first polymeric film layer capable of withstanding atemperature of at least 200 C for at least 10 min, (ii) a first adhesivelayer having an areal weight of from 2 to 40 gsm capable of activationat a temperature of from 75 to 200 degrees C., (iii) an inorganicrefractory layer, (iv) a second adhesive layer having an areal weight offrom 2 to 40 gsm capable of activation at a temperature of from 75 to200 degrees C., and (v) a second polymeric film layer capable ofwithstanding a temperature of at least 200 C for at least 10 min,wherein at least one of the first or second polymeric film layers isthermoplastic; wherein the inorganic refractory layer of (iii) comprisesplatelets in an amount of 100% by weight with a dry areal weight of 15to 50 gsm and a residual moisture content of no greater than 10 percentby weight.
 2. The laminate of claim 1 wherein the inorganic refractorylayer comprises vermiculite.
 3. The laminate of claim 1 wherein theinorganic refractory layer is perforated.
 4. The laminate of claim 3wherein the adhesive bond between inorganic refractory layer and eitherpolymeric film is at least 1.0 lb/in.
 5. The laminate of claim 4 whereinthe adhesion bond between inorganic refractory layer and eitherpolymeric film is at least 1.5 lb/in.
 6. The laminate of claim 1 whereinthe first and second polymeric film layer is a fluoropolymer, polyimide,polyetheretherketone, or polyetherketoneketone.
 7. The laminate of claim1 wherein the first and/or second polymeric film layer is metalized onat least one surface.
 8. The laminate of claim 1 wherein either thefirst or second or both adhesive layers optionally contain up to 40weight percent of a flame retardant ingredient.
 9. The laminate of claim1 wherein the adhesion bond between the inorganic refractory layer andthe first polymeric film is at least 0.5 lb/in.
 10. The laminate ofclaim 9 wherein the adhesion bond between the inorganic refractory layerand the first polymeric film is at least 0.8 lb/in.
 11. The laminate ofclaim 1 wherein the adhesive bond between the inorganic refractory layerand the second polymeric film is at least 0.25 lb/in.
 12. The laminateof claim 11 wherein the adhesion bond between the inorganic refractorylayer and the second polymeric film is at least 0.8 lb/in.
 13. Thelaminate of claim 1 wherein the inorganic refractory layer has a dryareal weight of from 20 to 35 gsm.
 14. The laminate of claim 1 whereinthe inorganic refractory layer has a moisture content of no greater than3%.
 15. A flame barrier layer in a vehicle or building structurecomprising the multilayer laminate of claim 1.